1. Technical Field
The present invention relates to a backlight unit, and more particularly, to a light emitting lamp which is capable of reducing a tube voltage thereof via an increased area of external electrodes while not reducing an effective light emitting region, and a backlight unit having the same.
2. Discussion of the Related Art
Of commonly used display devices, cathode ray tubes (CRTs) are mainly used in monitors of TVs, measuring instruments, information terminals, and the like. However, CRTs do not meet the requirements of compact-size and light-weight of electronic products due to their heavy weight and large size.
In the tendency towards compact-size and light-weight of a variety of electronic products, CRTs have limitations in reducing their weight and size. Examples of display devices to substitute for CRTs include liquid crystal display (LCD) devices utilizing electroluminescent optical effects, plasma display panels (PDPs) using gas discharge, and electroluminescence display (ELD) displays using electroluminescent effects. Of these display devices, in particular, LCD devices are being actively researched.
LCD devices have been actively developed as a substitute for CRTs because of a lot of outstanding advantages thereof, for example, light-weight, compact-size, and low energy consumption. Recently, LCD devices reach the stage of sufficiently implementing the role of flat panel display devices, and are most widely used as monitors of desktop computers and large-scale information display devices as well as monitors of laptop computers. Accordingly, demand for LCD devices is continuously increasing.
Since most LCD devices are light-receiving devices for regulating the intensity of light incident thereto from the outside to display pictures and images, they essentially require the use of additional light sources, namely, backlight units, for irradiating light onto LCD panels.
Generally, depending on the arrangement of cylindrical light emitting lamp(s), backlight units used as light sources of LCD devices are classified into edge-type backlight units and direct-type backlight units.
Firstly, in a conventional edge-type backlight unit in which a lamp unit is arranged at either lateral side of a light guide plate for guiding light emerged from the lamp unit, the lamp unit includes a light emitting lamp, lamp holders inserted to both ends of the lamp to protect the lamp, and a lamp reflection plate wrapped around the lamp, one side of the lamp reflection plate being fitted to a face of the light guide plate and adapted to reflect the light incident thereto from the lamp toward the light guide plate.
Such an edge-type backlight unit, in which a lamp unit is arranged at either lateral side of a light guide plate, is mainly applied to relatively small-sized LCD devices, such as monitors of laptop computers and desktop computers, and has a good light uniformity and long life-span, and is advantageous in achieving thinness of LCD devices.
On the other hand, as the size of LCD devices is increased to 20 inches or above, active developments on direct-type backlight units are being made nowadays. According to the direct-type backlight units, a plurality of lamps are arranged in one direction on a lower surface of a diffusion plate so that light is directly irradiated over the entire surface of an LCD panel.
The direct-type backlight unit has higher light use efficiency than the edge-type backlight unit, and therefore, is mainly employed in large-screen LCD devices requiring high brightness.
However, since LCD devices employing the direct-type backlight unit are used in large-sized monitors and television sets, the time of use thereof is longer than that of laptop computers, and the number of lamps used is greater than that of the edge-type backlight unit. Accordingly, the possibility that the lamps are not turned on due to an exhausted life span and failure thereof is more increased in the direct-type backlight unit as compared to the edge-type backlight unit.
Also, in the edge-type backlight unit in which lamp units are arranged at opposite sides of a light guide plate, respectively, even if one of lamps is not turned on due to an exhausted life and failure thereof, it has less serious effect except for deterioration in brightness on a screen. However, in the direct-type backlight unit in which a plurality of lamps are mounted on a lower surface of a screen, if one of the lamps is not turned on due to an exhausted life and failure thereof, a region where the lamp is not turned on is significantly darker than the remaining region. As a result, the region where the lamp is not turned on is clearly visible on the screen.
For this reason, LCD devices using the direct-type backlight unit requires frequent exchange of lamps, and therefore, should be designed to have a configuration suitable to disassemble and assemble the lamp unit.
As lamps for use in the edge-type and direct-type backlight units, there can be used, for example, electroluminescence (EL) lamps, light-emitting diodes (LEDs), cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamp (HCFLs), and external electrode fluorescent lamps (EEFLs).
Now, a conventional light emitting lamp will be explained with reference to the accompanying drawing.
FIG. 1 is a perspective view illustrating a conventional light emitting lamp.
As shown in FIG. 1, the conventional light emitting lamp, which is designated as reference numeral 11, includes a lamp tube 10, and first and second external electrodes 12a and 12b externally arranged at both ends of the lamp tube 10 to be aligned in a line with respect to each other.
The conventional light emitting lamp 11 is an external electrode fluorescent lamp of a type in which caps (namely, external electrodes) are wrapped around both ends of a light emitting tube and used as a capacitor electrode, whereby a plurality of lamps can be powered in parallel by use of a single inverter.
A tube voltage to be applied to the light emitting lamp 11 is inversely proportional to a total area of the first and second external electrodes 12a and 12b (namely, a contact area between the glass tube and the caps). Accordingly, the smaller the total area of the first and second external electrodes 12a and 12b, the greater the tube voltage.
If the area of the first and second external electrodes 12a and 12b is reduced, and thus, the tube voltage is increased, there is a risk of generation of ozone inside the lamp tube. Therefore, it is necessary to increase the area of the first and second external electrodes 12a and 12b for the sake of reliability.
However, where the length of the first and second external electrodes 12a and 12b is increased to achieve a greater area of the first and second external electrodes 12a and 12b, the external electrodes 12a and 12b may encroach on an effective light emitting region, resulting in deterioration in brightness and poor quality of image.